The invention relates to a device with a prosthesis implantable in the body of a patient, especially in a blood vessel or other body cavity, and designed as a hollow body. The prosthesis is compressible against the action of restoring spring forces down to a cross section which is reduced relative to an (expanded) operating position. The prosthesis may be also automatically expanding to a cross section corresponding to the operating position following removal of the restraining forces effecting the compression.
Devices of this type are known, and serve for percutaneous implantation of vascular prostheses in particular. Prostheses which are introducible percutaneously and expand in the lumen are either expandable mechanically by means of a known balloon catheter from a small radius to the larger radius to hold a vascular lumen open, or they expand automatically following previous compression prior to implantation by spring force, due to spring pretensioning generated during compression.
Various systems are already known for inserting self-expanding vascular prostheses which are under spring force into the body of a patient, and to implant or anchor them in the vessel by removing the restraining force.
The commonest method, which is described in EP-A-0 183 372, consists in compressing an endoprosthesis, made in the form of a tubular hollow body, to a reduced cross section and then pushing it in the compressed state, using a so-called pusher, through a catheter previously introduced into a vessel until they are in the correct position in the vessel. However, this system suffers from the disadvantage that a considerable expenditure of force is required to push the prosthesis through the catheter because its displacement is counteracted by considerable frictional forces.
Another method (not confirmable by publications) consists in retracting a sheath covering the endoprosthesis and holding the latter together, in the vessel at the implantation site. Here again there is the disadvantage that high frictional forces must be overcome. Moreover, the tube system is quite rigid because of the sheath covering the prosthesis, making introduction into a vessel through curves very difficult.
In another system (U.S. Pat. No. 4,732,152) a woven and spring-tensioned prosthesis is held together in the compressed state by a double sheath, sealed at the distal end. This sheath is retracted from the folded prosthesis like a stocking being pulled off the foot of a wearer. To reduce the friction which then occurs, liquid can be introduced between the two sheath layers. This system, which initially appears elegant because of the reduction of the frictional resistances, is extremely cumbersome to handle however and requires two persons to operate.
On the other hand, the invention is intended to provide an especially simple and readily operable device for implantation of a prosthesis made in the form of a hollow body, with a vascular prosthesis envisioned in particular.
This goal is achieved by virtue of the fact that in the device according to the preamble of claim 1 the prosthesis is surrounded by a sheath which can be pulled off it, said sheath consisting of at least one through thread, and compressed to a reduced cross section, and by the fact that at least one drawstring is provided, said drawstring being laid so it extends away from the sheath holding the prosthesis in its radially compressed state, the thread forming said sheath being retractable.
In the invention, the prosthesis is therefore held in its radially compressed state by means of this external sheath and reaches its intended expansion position only after removal of this sheath, which is designed to be pulled off, thanks to the pretensioning force generated during compression.
The sheath can be in particular a meshwork produced by crocheting, knotting, tying, or other methods of mesh formation.
Advantageously the prosthesis, held by the sheath which can be pulled off in the radially compressed state, can be received on a probe, or a flexible guide wire, and advanced thereon. In one design of a device of this kind, implantation is accomplished by introducing the guide wire in known fashion into a vessel and then advancing the prosthesis, held in a radially compressed state, along the guide wire, said wire being advanced for example by means of a sleeve likewise advanced over the guide wire and engaging the end of the prosthesis away from the insertion end thereof.
Another improvement, on the other hand, provides that the prosthesis, held in the radially compressed state by the sheath which can be pulled off, is held in an axially fixed position on the insertion end of a probe. Specifically, this probe can be a catheter advanced over a guide wire.
Even with the axially fixed mounting of the prosthesis, held in the compressed state, on the insertion end of a probe or a catheter, implantation takes place in simple fashion with the probe or catheter being advanced together with the prosthesis mounted on the insertion end, for example under the control of x-rays, up to the implantation site, and then by pulling off the sheath, made for example as a covering meshwork, the prosthesis is exposed and implanted in the proper location by its automatic expansion.
In mounting the prostheses on the insertion ends of probes or catheters, it has been found to be advantageous for the prosthesis to be mounted on a non-slip substrate surrounding the probe or catheter, so that undesired slipping and sliding during the release of the thread material forming the meshwork cannot occur.
Advantageously, the self-expanding prosthesis can be a tube made by crocheting, knitting, or other methods of mesh formation, composed of metal and plastic thread material with good tissue compatibility, said tube being compressible radially against the action of pretensioning forces and automatically expanding into its operating position after the restraining forces are removed, and then remaining in the expanded position.
In the case of the prosthesis designed as meshwork, according to a logical improvement, successive rows of mesh can be made alternately of resorbable thread material and non-resorbable thread material. This means that within a predetermined period of time after implantation, the resorbable thread material will be dissolved and the prosthesis parts, then consisting only of non-resorbable thread material, will remain in the patient""s body. These remaining components form circumferential rings of successive open loops. This avoids thread intersections which could exert undesirable shearing forces on surrounding and growing tissue coatings.
In the improvement just described, drugs can also be embedded in the resorbable thread material so that the prosthesis constitutes a drug deposit which gradually dispenses drugs during the gradual dissolution of the resorbable thread material.
An especially advantageous improvement on the invention is characterized by making the tubular meshwork holding the prosthesis in the compressed state in such a way that the mesh changes direction after each wrap around the prosthesis and when successive meshes are pulled off, the thread sections forming the latter separate alternately to the right and left from the prosthesis.
The advantage of this improvement consists in the fact that the mesh wrapped successively and alternately left and right around the prosthesis can be pulled off without the thread material becoming wrapped around the probe holding the prosthesis or a catheter serving as such, or undergoing twisting, which would make further retraction of the thread material more difficult because of the resultant friction.
It has also been found to be advantageous in the improvement described above for the loops or knots of the mesh wrapped successively around the prosthesis and capable of being pulled off, to be located sequentially with respect to one another or in a row running essentially axially.
Another important improvement on the invention provides for the drawstring to extend away from the mesh surrounding the insertion end of the prosthesis, and therefore the prosthesis, as the meshwork is pulled off its distal end, gradually reaches its expanded position.
In this improvement, the thread material to be pulled off when the prosthesis is tightened can never enter the area between the already expanded part of the prosthesis and the wall of a vessel for example. The thread material to be pulled off instead extends only along the part of the mesh which has not yet been pulled off and thus in the area of the prosthesis which is still held in the compressed position.
The ends of the thread material forming the meshwork can be held by releasable knots, in the form of so-called slip knots for example, and thereby have their releasability preserved. One especially simple means that has been found for axial mounting of the prosthesis on a probe or on a catheter serving as such is for the beginning of the thread material forming the meshwork and an end mesh to be pinched in holes in the probe or catheter, yet capable of being pulled out of their pinched positions by means of the drawstring. The beginning of the thread material can be pinched between the probe and the cuff mounted held on the latter, however.
The cuff material is held especially securely, but at the same time in such a way that it can be easily pulled off, if from the knot of the mesh of the first mesh on the pull-off side of the meshwork, a loop passed through a hole extends, one end of said loop making a transition in the vicinity of the above knot to the drawstring. As a result, this loop can be pulled off by means of the drawstring through the above-mentioned knot and then all of the mesh forming the meshwork can be pulled off in succession.
According to another logical improvement on the invention, the prosthesis can also be held in its radially compressed position by means of a meshwork applied from the distal end of the probe or catheter and extending over the insertion end of the prosthesis and by means of a meshwork that extends in the direction opposite the proximal end and also extends over the end mesh of the first meshwork. It has been found advantageous in this connection for the two meshworks to be capable of being pulled off in opposite directions from their loop-shaped end meshes by means of drawstrings.
In a design of this kind, following correct placement of the prosthesis mounted on a probe or a catheter in a vessel, the meshwork applied from the distal end is pulled off first, beginning with the end mesh removed from the distal end and then advancing gradually until this meshwork is removed completely and the thread material is retracted. Then the meshwork applied from the proximal end is pulled off, starting with the end mesh toward the distal end and then advancing toward the proximal end. It is obvious that when the meshwork is pulled off in this way, the self-expanding prosthesis is expanded gradually, starting at its distal end, into its intended operating position.
In another important embodiment, the sheath that holds the prosthesis in its radially compressed position consists of loops surrounding the prosthesis and spaced axially apart, said loops being formed by the thread material, pulled through a hole in the prosthesis, of a thread guided along inside the prosthesis, with the ends of the loops each being brought back through a hole, adjacent to the first hole in the circumferential direction, into the interior of the prosthesis, and a warp thread, likewise running along the inside of the prosthesis and guided through the ends of the loops, holds in the loops in their wrapping positions. It is clear that in this design the prosthesis is released by pulling the warp thread out of the end segments of the loops, and that the thread material forming the loops, like the warp thread, can be retracted in simple fashion. In a similar improvement on the invention, the sheath holding the prosthesis in its radially compressed position consists of loops which are axially spaced apart and are wrapped around the prosthesis, said loops being formed by thread material, pulled through a hole in the prosthesis, of a thread guided along inside the prosthesis, with the ends of the loops each being brought back into the interior of the prosthesis through holes spaced axially from the first hole, and held in place by the fact that a loop formed from the thread material running inside the prosthesis is pulled through each loop end brought back into the prosthesis, said loop then being brought out through a hole following in the axial direction, then being wrapped around the prosthesis and brought back in the same manner with its loop end passing through a hole into the prosthesis and being secured in this position. In this design also, the pulling off of the sheath holding the prosthesis in its radially compressed position is accomplished in simple fashion by means of the thread extending from the last loop, from which the loops surrounding the prosthesis are formed.
For especially tight wrapping and the resultant compression of the prosthesis, it has also been found advantageous to use shrinkable thread material to form the meshwork. The meshwork that can be pulled off can also consist of a plurality of threads running parallel to one another.
Another important improvement on the invention provides that between the prosthesis and the sheath holding the latter in the radially compressed state, at least one additional sheath is provided which loosely fits around the prosthesis and allows a partial expansion of the prosthesis when the outer sheath is pulled off, and is itself subsequently capable of being pulled off.
This improvement is also one that involves a sheath, surrounding the prosthesis loosely and with a certain amount of play, being mounted on said prosthesis, which can be a meshwork, with the prosthesis and the inner sheath being surrounded closely by an outer sheath which holds the prosthesis, together with the sheath mounted directly on it, in the radially compressed state. The prosthesis is consequently surrounded by two layers, so to speak, and after the outer sheath is stripped, can expand only within the limits set by the inner sheath. The final implantation is then accomplished by stripping the inner sheath, i.e. in stages.
Of course, several meshworks surrounding one another with a certain amount of play can be provided, which permit expansion of the prosthesis in several successive stages.
Within the scope of the invention, the spaces between the meshes of a meshwork surrounding the prosthesis and holding it in the compressed state can be filled and smoothed with gelatin or a similar substance which dissolves in the body of a patient. This facilitates introduction of such a device.
According to yet another improvement, at least one end of the prosthesis can be surrounded in the compressed state by a cuff, said end, because of the axial shortening of the prosthesis that takes place during expansion, escaping the grip exerted by the cuff. A cuff of this kind can be mounted permanently on the probe and/or a catheter, with the open side facing the prosthesis, for example on the side toward the distal end. This produces a smooth transition that facilitates introduction, at the end of the prosthesis which is at the front in the insertion device.
For improved attachment of the prosthesis to a probe or to a catheter serving as same, the end of the prosthesis facing away from the insertion end can abut at a radially projecting step or shoulder or a cuff mounted on the probe or catheter.
Yet another improvement on the invention provides that when a catheter is used as a probe, the drawstring is introduced through a hole passing through the catheter wall in the vicinity of one end of the prosthesis, enters the lumen of the catheter, extends through the latter, and extends beyond the end of the catheter.
However, a double-lumen catheter can also serve as a probe with one lumen serving to advance the catheter over a guide wire and the other lumen being used to guide the drawstring.
When using a catheter with one or two lumina as a probe, with the drawstring passing through the catheter lumen, assurance is provided that the walls of the vessels or other body cavities in which a prosthesis is to be implanted cannot be damaged by the drawstring and/or, when the meshwork is stripped, by the thread material, which is then pulled back through the catheter lumen.
It has also proven to be advantageous for the drawstring and/or the thread material of the meshwork to be provided with a friction-reducing lubricant.
In addition, at least the drawstring can be made in the form of a metal thread or provided with an admixture of metal, so that good visibility with x-rays is ensured.
Finally, according to yet another improvement, the prosthesis, kept in the radially compressed position by the strippable sheath, can expand to resemble a trumpet at its proximal end in the expanded state following removal of the sheath,. This prosthesis design is important for implants in the vicinity of branches in the vessels, because there is always the danger of the prosthesis slipping into the branching vessel. In view of the trumpet-shaped expansion at the proximal end, however, such slipping during implantation is effectively suppressed when the sheath surrounding the prosthesis is stripped off the proximal end.